Genomic and palaeoclimatic data reveal Pleistocene adaptation and diversification of non-model bluegrasses (Poa sect. Stenopoa) in cold, arid environments.

Rapid plant radiations under climatic oscillations are widely recognised, yet our understanding of how taxonomically complex, polyploid-rich lineages diversify in extreme environments remains limited. Here, we investigated non-model Eurasian bluegrasses (Poa sect. Stenopoa), a challenging group inhabiting cold deserts, alpine grasslands, and semi-arid steppes. We utilised DArTseq genotyping of 373 individuals to infer phylogenetic relationships, identify key adaptive traits, test evolutionary scenarios, estimate demographic histories, and integrate palaeoclimatic niche reconstructions to trace the role of glacial-interglacial cycles in shaping diversification. Our findings reveal three major genetic groups that diverged during the Middle Pleistocene, partly uncoupled from morphological differentiation. Demographic analyses indicate divergence from a small ancestral population, followed by niche partitioning, secondary contact, and episodic gene flow promoted by glacial oscillations. Morphological traits associated with cold and arid tolerance further demonstrate ecological adaptation beyond genetic divergence. This research highlights how climate fluctuations and episodic hybridisation structure the diversification of this complex polyploid lineage. Moreover, our results illustrate a general framework for resolving evolutionary histories of challenging taxonomic groups, underscoring that integrative genomic and palaeoclimatic approaches can reveal mechanisms of rapid speciation in non-model taxa under changing environments.